CN100526821C - Thin film type optical fiber temperature sensor and its temperature sensing method - Google Patents

Abstract

The present invention relates to optical measurement instrument, and aims at providing one kind of thin film type optical fiber temperature sensor with high temp sensitivity and high reliability and its temperature sensing method. Structurally, the optical fiber temperature sensor includes one optical fiber with one light signal incoming end face and one light signal outgoing end face, and the light signal outgoing end face is coated with one optical medium film, which has reflectivity changing with temperature. The thin film type optical fiber temperature sensor operates on that the refractivity and thus the reflectivity or the transmissivity of the optical medium film vary with temperature.

Description

A kind of thin film type optical fiber temperature sensor and temperature sensing method thereof

Technical field

The present invention relates to the optical gauge field, say so more specifically a kind of thin film type optical fiber temperature sensor and temperature sensing method thereof.

Technical background

In strong-electromagnetic field and high-voltage system, temperature is to need one of important physical amount of measuring and controlling, and traditional electric detecting technology such as thermopair etc. can't use with producing danger such as short circuit sets off an explosion owing to having electromagnetic noise.Fibre optic temperature sensor have good, the anti-strong electromagnetic of electrical insulation capability, safe and reliable, volume is little, in light weight, be specially adapted to use under strong-electromagnetic field, high voltage and poisonous and harmful, the rugged surroundings such as inflammable and explosive, wide application prospect is arranged.

The domestic and international at present research for fibre optic temperature sensor is divided into both direction.The first kind is exactly the light transmission type fibre optic temperature sensor.Light transmission type (absorbs light intensity, heat radiation, variations in refractive index, scattering), wavelength (fluorescence, photoluminescence), plane of polarization (birefringence), temperature signal is used as in time variation (fluorescence) etc., just utilize the channel effect of light transmission fiber, on an end face of optical fiber, dispose other temperature sensor, and be coupled together, constitute Fibre Optical Sensor with optical fiber.Second class is exactly the sensing type fibre optic temperature sensor, is to utilize phase place (interference), and intensity (scattering) is as temperature signal, and the characteristic that the physical parameter of utilizing optical fiber self to be had changes along with temperature variation constitutes Fibre Optical Sensor.Though the light transmission type sensor is relatively poor to the sensitivity of temperature detection, the reliability height wherein utilizes fluorescent absorption, and thermal-radiating fibre optic temperature sensor has reached realistic scale.Sensing type fibre optic temperature sensor highly sensitive, but because to the pressure beyond the temperature, the variation of mechanical quantity such as vibration is also very sensitive, therefore, its reliability is an open question still.

Summary of the invention

The objective of the invention is to overcome shortcoming of the prior art, provide a kind of temperature sense sensitivity, thin film type optical fiber temperature sensor that reliability is high and temperature sensing method thereof.

At first the invention discloses a kind of thin film type optical fiber temperature sensor, structure is to comprise one section optical fiber, optical fiber has a light signal incident end face and light signal outgoing end face, is coated with on light signal outgoing end face that one deck reflectivity varies with temperature and the optical thin film that changes.Thin film type optical fiber temperature sensor mainly is a characteristic of utilizing the refractive index of optical thin film medium to change along with temperature variation, and then has influence on special wavelength light wave reflection rate or transmission change and a kind of novel optical fiber temperature sensor of constituting.The strong-electromagnetic field or the high voltage that can not be subjected to when the present invention uses producing in the measuring process of temperature influence, the sensitivity that has the sensing type fibre optic temperature sensor simultaneously, and because optical film thickness is very little, therefore the present invention can not be subjected to ambient pressure, the influence of mechanical quantity such as vibration has very high stability.

The present invention further provides a kind of temperature sensing method that is suitable for described thin film type optical fiber temperature sensor, by obtaining reflectivity or transmitance, obtain ambient temperature with the curve that ambient temperature changes according to optical thin film reflectivity or transmitance at the optical thin film of fiber end face.This is different from existing sensing type fibre optic temperature sensor, is to utilize phase place (interference), and intensity (scattering) is utilized the optical fiber self property to change with variation of temperature and obtained temperature as temperature signal, and this has also determined the stability advantage that the present invention had.The curve that described optical thin film reflectivity or transmitance change with ambient temperature is the variation by measurement specific wavelength reflectivity or transmitance under the demarcation temperature, and will organize the corresponding data calibration curve that match obtains on coordinate system more.The mode that adopts the demarcation method of temperature to obtain calibration curve is the most direct a kind of mode, and is a kind of mode that meets each actual temp sensor own characteristic most, can further reduce because the error that technological reason produced.

Said method specifically may further comprise the steps:

1. thin film type optical fiber temperature sensor is placed the temperature environment that is detected, light signal is from the light signal incident end face incident of optical fiber;

2. survey light signal at the reflective light intensity or the transmitted light intensity that are coated on the optical thin film on the optical fiber light signal outgoing end face;

3. the reflectivity of calculating optical film or transmissivity;

4. the curve that changes with ambient temperature according to the corresponding optical thin film reflectivity of above-mentioned reflectivity or transmissivity or transmitance obtains to be detected the temperature of environment.

The inventive method is simple to be realized easily, and is applicable to and adopts computing machine to carry out measurements and calculations, helps improving the automaticity of measuring system, makes the simpler and easy and hommization of temperature survey.

The sensor ends of above-mentioned thin film type optical fiber temperature sensor is to form by the optical thin film that is coated with at fiber end face, for making reflectivity or transmittance curve have good linearty, is convenient to measure.The present invention has selected light cutoff filter rete structure as the standard at the fiber end face plated film.

The film structure of described optical thin film is

Or

, H represents that optical thickness is the high refractive index layer of the centre wavelength of 1/4th films system, L represents that optical thickness is the low-index layer of 1/4th centre wavelengths.M is the multiplicity of basic cycle, is generally 5＜m＜10, can decide according to the coating machine of concrete employing, adopts existing general coating machine, and its optimal values is 6 or 7.The light cutoff filter rete is made up of the material of high and low refractive index, and environment temperature mainly is that (n, k d) realize for optical constant by changing the device of optical film to the influence of device of optical film temperature stability.At visible, near-infrared band, described low refractive index dielectric layer and high index of refraction layer material adopt oxide, fluoride, sulfide or telluride.The thermal refractive index coefficient of this class material is suitable with its thermal expansivity, and its temperature drift is mainly by refractive index n and geometric thickness d acting in conjunction decision, and influence is mainly by refractive index n and geometric thickness d acting in conjunction decision.The material that the refractive index temperature coefficient is bigger, the temperature drift of the device of optical film are mainly caused by the variation of refractive index n.Described low-refraction layer material is SiO ₂, NaF or MgF ₂, the high index of refraction layer material is TiO ₂, PbTe or ZeS, the spectrum property of light cutoff filter rete is by the refractive index and the thickness decision of each tunic.During the variation of environment temperature, the optical characteristics of described optical thin film can change along with the variation of environment temperature.The peak transmittance that this variation mainly is characterized by optical thin film changes, and the position of cutoff wavelength or centre wavelength drifts about, bandwidth change etc.

The present invention has following outstanding substantive distinguishing features and obvious improvement with respect to prior art.

1. sensor construction disclosed by the invention has little, the lightweight advantage of volume, is specially adapted to the temperature survey under the rugged surroundings such as strong-electromagnetic field, high voltage;

2. have very high sensitivity and good repeatability and temperature stability;

3. the inventive method is simply easy to implement, can be applicable to computer control, reduces error.

Description of drawings

The film of Fig. 1 sensor of the present invention is a reflectance curve;

Fig. 2 is the reflectivity-temperature relation curve of film;

Fig. 3 is a sensor construction synoptic diagram of the present invention;

Fig. 4 is the sensor measuring system schematic diagram;

Fig. 5 is the reflectivity-temperature relation curve of Fibre Optical Sensor.

Embodiment

The present invention will be further described in detail below in conjunction with accompanying drawing.

The principle explanation

The cutoff wavelength of the logical light cutoff filter rete structure of band can be stated as:

$\frac{{\mathrm{\λ}}_0}{{\mathrm{\λ}}_c}=1\±\frac{2}{\mathrm{\π}}{\sin }^{-1}\left(\frac{{\mathrm{\η}}_H-{\mathrm{\η}}_L}{{\mathrm{\η}}_H+{\mathrm{\η}}_L}\right)---\left(1\right)$

λ wherein ₀It is a reference wavelength.

Its rejection zone width is:

$\mathrm{\Δg}=\frac{2}{\mathrm{\π}}{\sin }^{-1}\left(\frac{{\mathrm{\η}}_H-{\mathrm{\η}}_L}{{\mathrm{\η}}_H+{\mathrm{\η}}_L}\right)---\left(2\right)$

Corresponding transmissivity is:

$R=\frac{I_0^{-}}{I_0^{+}}={\left|r\right|}^2={\left|\frac{{\mathrm{\η}}_{0}B-C}{{\mathrm{\η}}_{0}B+C}\right|}^2---\left(3\right)$

Δ g is about η as can be seen from the above _HAnd η _LFunction, and when normal incidence, η _H=n _H, η _L=n _LAnd n _HAnd n _LBe again the function of temperature T, rejection zone width Δ g also is the function of temperature T so, can be write as following form:

Δg＝f(T) (4)

Following formula is differentiated,,

$\frac{d\left(\mathrm{\Δg}\right)}{\mathrm{dT}}=\frac{\mathrm{df}\left(T\right)}{\mathrm{dT}}=u\left(T\right)---\left(5\right)$

When temperature variation, the rejection zone width can change, and the reflectivity of certain wave strong point also can change.The temperature variant rule of refractive index of general material is linear, and the reflectivity of transmittance graph edge is also linear with variation of temperature.Based on this variation characteristic, the present invention designs a kind of novel thin film type optical fiber sensor.

Consider that the general designed used light signal center wavelength of sensor is 1310nm, so in bare fibre end face plated film, make that near the reflectance curve the 1310nm has good linearty.The present invention has selected the film layer structure of cutoff filter as the standard at the fiber end face plated film.Select TiO ₂As high-index material, SiO ₂As low-index material, and the centre wavelength that earlier selected film is is 1080nm.Incident medium is a glass, and transmission medium is an air.Film structure is

By analog computation, draw the reflectance curve under the different wave length, as shown in Figure 1.The reflectance curve of this film system has good linearty near 1310nm.Selected this section curve is as the perform region of sensor.When temperature changed, because the material change of refractive, this section curve can produce drift, thereby makes the transmitance of certain wave strong point also produce corresponding variation, as shown in Figure 2, and T wherein ₁＜T ₂＜T ₃And T ₃-T ₂=T ₂-T ₁By demarcating the variation relation of transmitance under temperature and the specific wavelength, can obtain a calibration curve.Utilize calibration curve,, just can find corresponding temperature, thereby reach the effect of sensing temperature when the value that records transmitance.The film structure that designs previously is coated on the single-mode fiber end face, prepares the thin film type optical fiber temperature sensor of design.

The structure of fibre optic temperature sensor as shown in Figure 3, sensor is made up of the high and low refractive index period film 2 that is plated in bare fibre 1 end face, film structure is High-index material is TiO ₂, low-index material is SiO ₂, the multiplicity of basic cycle is 6, the centre wavelength that selected film is is 1080nm.As previously described shown in Figure 2 of the reflectance curve of film system, the transmittance curve of film system at 1260nm to the better linearity degree is arranged between 1360nm.When temperature variation, the spectral characteristic of film system will change, and wherein 1260nm has reasonable linearity to reflectivity between 1360nm and variation of temperature curve.By the reflectivity of survey sensor, the ambient temperature that sensor detects will be obtained.

Utilize sensor of the present invention, build Sensor Analog Relay System experiment measuring system according to Fig. 4.In this experimental system, select for use centre wavelength be the LD light source 3 of 1310nm as signal source, the 1830-C type photodetector 5 that three-dB coupler 4 and Newport company produce.The light that LD light source 3 sends enters thin film type optical fiber temperature sensor 6 of the present invention through three-dB coupler 4, the reflected light of thin film type optical fiber temperature sensor 6 will be once more by three-dB coupler 4 enter photodetector 5, reflected light signal detects through photodetector 5.Another of coupling mechanism 4 inserts in the index-matching fluid 8 to eliminate end face reflection.Thin film type optical fiber temperature sensor 6 is put in the water-bath 9, changed its environment temperature by the temperature that changes water-bath 9, the temperature of thin film type optical fiber temperature sensor 6 can directly be read from water temperature.Experiment finds, when the temperature variation of thin film type optical fiber temperature sensor 6, the light intensity that photodetector 5 detects is also changing, and the variation of reflectivity becomes reasonable linear relationship with the temperature variation of thin film type optical fiber temperature sensor 6.The data that obtain are just analyzed by computing machine 7 can draw the temperature value that thin film type optical fiber temperature sensor 6 detects.Want in actual use earlier the thin film type optical fiber temperature sensor 6 that designs to be carried out the temperature survey calibration.

The optical fiber transmissivity that grows based on the top certain wave of surveying and the linear relationship of temperature have been carried out the experiment of thin film type optical fiber temperature sensor 6 according to the experimental system figure of Fig. 4.The reflectivity of the thin film type optical fiber temperature sensor 6 of the 1310nm that records and the relation curve of temperature, as shown in Figure 5.Experimental result shows that the measuring accuracy of sensor of the present invention can reach 1 ℃, has also shown good stable and repeatability in repeatedly measuring.If by selecting higher thermal refractive index coefficient material such as lead telluride, zinc sulphide etc. for use, measuring accuracy of the present invention will be further enhanced.

Claims (5)

1. a thin film type optical fiber temperature sensor is characterized in that comprising one section optical fiber, and optical fiber has a light signal incident end face and light signal outgoing end face, is coated with on light signal outgoing end face that one deck reflectivity varies with temperature and the optical thin film that changes; The film structure of described optical thin film is the light cutoff filter film structure, and its film structure is

Or

H represents that optical thickness is the high refractive index layer of the centre wavelength of 1/4th films system, L represents that optical thickness is the low-index layer of 1/4th centre wavelengths, m is the multiplicity of basic cycle, and light signal center wavelength is 1310nm, and the centre wavelength of film system is 1080nm.

2. thin film type optical fiber temperature sensor according to claim 1 is characterized in that multiplicity 5＜m＜10 of described basic cycle.

3. thin film type optical fiber temperature sensor according to claim 1 is characterized in that described low-index layer and high index of refraction layer material are oxide, fluoride, sulfide or telluride.

4. thin film type optical fiber temperature sensor according to claim 3 is characterized in that described low-refraction layer material is SiO ₂, NaF or MgF ₂, described high index of refraction layer material is TiO ₂, PbTe or ZeS.

5. temperature sensing method that is applicable to the described thin film type optical fiber temperature sensor of claim 1, it is characterized in that obtaining reflectivity or transmitance at the optical thin film of fiber end face, obtain ambient temperature according to optical thin film reflectivity or transmitance with the curve that ambient temperature changes, the curve that described optical thin film reflectivity or transmitance change with ambient temperature is by demarcating the variation of measuring specific wavelength reflectivity or transmitance under the temperature, and will organize the corresponding data calibration curve that match obtains on coordinate system more, specifically may further comprise the steps:

1. thin film type optical fiber temperature sensor is placed the temperature environment that is detected, light signal is from the light signal incident end face incident of optical fiber;

2. survey light signal at the reflective light intensity or the transmitted light intensity that are coated on the optical thin film on the optical fiber light signal outgoing end face;

3. the reflectivity of calculating optical film or transmissivity;

4. the curve that changes with ambient temperature according to the corresponding optical thin film reflectivity of above-mentioned reflectivity or transmissivity or transmitance obtains to be detected the temperature of environment.

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